In related art, when a system is configured so that an in-vehicle camera device mounted on a car and so on is connected to a monitor device installed on the car to allow the monitor device to display taken video, the camera device is generally connected to the monitor device by a control line in addition to a transmission line for video. When control data can be transmitted from the monitor device to the camera device due to the connection by the control line, for example, power on/off, adjustment of brightness, switching of functions and so on in the camera device can be controlled on the side of the monitor device.